In a data rate converter, input data received in series synchronously with an input clock signal is converted into parallel data so as to be written into a memory, and the written parallel data is read from the memory and converted into serial data synchronously with an output clock signal so as to be outputted. Clock pulses of the input clock signal are counted to obtain an input count value. A ready signal is produced based on the input count value for allowing the start of reading the parallel data from the memory. The ready signal has a pulse width greater than two periods of the output clock signal. A trigger signal is produced upon detection of the second leading or trailing edge of the output clock signal within the pulse width of the ready signal. In response to the trigger signal, clock pulses of the output clock signal are counted to obtain an output count value. A read signal is produced based on the output count value for reading the parallel data from the memory.